<%--
  Created by IntelliJ IDEA.
  User: LENOVO
  Date: 2020/5/13
  Time: 13:43
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--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>流星雨</title>
    <script>

        var context;

        var arr = new Array();
        var starCount = 800;

        var rains = new Array();
        var rainCount =20;

        //初始化画布及context
        function init(){
            //获取canvas
            var stars = document.getElementById("stars");
            windowWidth = window.innerWidth; //当前的窗口的高度
            stars.width=windowWidth;
            stars.height=window.innerHeight;
            //获取context
            context = stars.getContext("2d");
        }

        //创建一个星星对象
        var Star = function (){
            this.x = windowWidth * Math.random();//横坐标
            this.y = 5000 * Math.random();//纵坐标
            this.text=".";//文本
            this.color = "white";//颜色

            //产生随机颜色
            this.getColor=function(){

                var _r = Math.random();

                if(_r<0.5){
                    this.color = "#333";
                }else{
                    this.color = "white";
                }

            }

            //初始化
            this.init=function(){
                this.getColor();
            }
            //绘制
            this.draw=function(){
                context.fillStyle=this.color;
                context.fillText(this.text,this.x,this.y);
            }

        }

        //画月亮
        function drawMoon(){
            var moon = new Image();
            moon.src = "./images/meteor/moon.jpg"
            context.drawImage(moon,-5,-10);
        }



        //页面加载的时候
        window.onload = function() {

            init();
            //画星星
            for (var i=0;i<starCount;i++) {
                var star = new Star();
                star.init();
                star.draw();
                arr.push(star);
            }

            //画流星
            for (var i=0;i<rainCount;i++) {
                var rain = new MeteorRain();
                rain.init();
                rain.draw();
                rains.push(rain);
            }

            drawMoon();//绘制月亮
            playStars();//绘制闪动的星星
            playRains();//绘制流星

        }

        //星星闪起来
        function playStars(){
            for (var n = 0; n < starCount; n++){
                arr[n].getColor();
                arr[n].draw();
            }

            setTimeout("playStars()",100);
        }


        /*流星雨开始*/

        var MeteorRain = function(){
            this.x = -1;
            this.y = -1;
            this.length = -1;//长度
            this.angle = 30; //倾斜角度
            this.width = -1;//宽度
            this.height = -1;//高度
            this.speed = 1;//速度
            this.offset_x = -1;//横轴移动偏移量
            this.offset_y = -1;//纵轴移动偏移量
            this.alpha = 1; //透明度
            this.color1 = "";//流星的色彩
            this.color2 = "";  //流星的色彩
            /****************初始化函数********************/
            this.init = function () //初始化
            {
                this.getPos();
                this.alpha = 1;//透明度
                this.getRandomColor();
                //最小长度，最大长度
                var x = Math.random() * 80 + 150;
                this.length = Math.ceil(x);
//                  x = Math.random()*10+30;
                this.angle = 30; //流星倾斜角
                x = Math.random()+0.5;
                this.speed = Math.ceil(x); //流星的速度
                var cos = Math.cos(this.angle*3.14/180);
                var sin = Math.sin(this.angle*3.14/180) ;
                this.width = this.length*cos ;  //流星所占宽度
                this.height = this.length*sin ;//流星所占高度
                this.offset_x = this.speed*cos ;
                this.offset_y = this.speed*sin;
            }

            /**************获取随机颜色函数*****************/
            this.getRandomColor = function (){
                var a = Math.ceil(255-240* Math.random());
                //中段颜色
                this.color1 = "rgba("+a+","+a+","+a+",1)";
                //结束颜色
                this.color2 = "black";
            }


            /***************重新计算流星坐标的函数******************/
            this.countPos = function ()//
            {
                //往左下移动,x减少，y增加
                this.x = this.x - this.offset_x;
                this.y = this.y + this.offset_y;
            }

            /*****************获取随机坐标的函数*****************/
            this.getPos = function () //
            {
                //横坐标200--1200

                this.x = Math.random() * window.innerWidth; //窗口高度
                //纵坐标小于600
                this.y = Math.random() * window.innerHeight;  //窗口宽度
            }
            /****绘制流星***************************/
            this.draw = function () //绘制一个流星的函数
            {
                context.save();
                context.beginPath();
                context.lineWidth = 1; //宽度
                context.globalAlpha = this.alpha; //设置透明度
                //创建横向渐变颜色,起点坐标至终点坐标
                var line = context.createLinearGradient(this.x, this.y,
                    this.x + this.width,
                    this.y - this.height);



                //分段设置颜色
                line.addColorStop(0, "white");
                line.addColorStop(0.3, this.color1);
                line.addColorStop(0.6, this.color2);
                context.strokeStyle = line;
                //起点
                context.moveTo(this.x, this.y);
                //终点
                context.lineTo(this.x + this.width, this.y - this.height);
                context.closePath();
                context.stroke();
                context.restore();
            }
            this.move = function(){
                //清空流星像素
                var x = this.x+this.width-this.offset_x;
                var y = this.y-this.height;
                context.clearRect(x-3,y-3,this.offset_x+5,this.offset_y+5);
//                  context.strokeStyle="red";
//                  context.strokeRect(x,y-1,this.offset_x+1,this.offset_y+1);
                //重新计算位置，往左下移动
                this.countPos();
                //透明度增加
                this.alpha -= 0.002;
                //重绘
                this.draw();
            }

        }

        //绘制流星
        function playRains(){

            for (var n = 0; n < rainCount; n++){
                var rain = rains[n];
                rain.move();//移动
                if(rain.y>window.innerHeight){//超出界限后重来
                    context.clearRect(rain.x,rain.y-rain.height,rain.width,rain.height);
                    rains[n] = new MeteorRain();
                    rains[n].init();
                }
            }
            setTimeout("playRains()",2);
        }


        /*流星雨结束*/
    </script>
    <style type="text/css">
        body{
            background-color: black;
        }
        body,html{width:100%;height:100%;overflow:hidden;}
    </style>
</head>
<body>
<canvas id="stars"></canvas>
</body>
</html>
